An axial flow, gas turbine engine typically has a compression section, a combustion section, and a turbine section. An annular flow path for working medium gases extends axially through these sections of the engine. A stator assembly extends about the annular flow path for confining the working medium gases to the flow path and for directing the working medium gases along the flow path.
As the gases are passed along the flow path, the gases are pressurized in the compression section and burned with fuel in the combustion section to add energy to the gases. The hot, pressurized gases are expanded through the turbine section to produce useful work. A major portion of this work is used as output power, such as for driving a free turbine or developing thrust for an aircraft.
A remaining portion of the work generated by the turbine section is not used for output power. Instead, this portion of the work is used in the compression section of the engine to compress the working medium gases. The engine is provided with a rotor assembly for transferring this work from the turbine section to the compression section. The rotor assembly has arrays of rotor blades in the turbine section for receiving work from the working medium gases. The rotor blades have airfoils that extend outwardly across the working medium flow path and that are angled with respect to the approaching flow to receive work from the gases and to drive the rotor assembly about the axis of rotation. The stator assembly has arrays of stator vanes which extend inwardly across the working medium flow path between the arrays of rotor blades. The stator vanes direct the approaching flow to the rotor blades at a desired angle.
The stator assembly further includes an outer case and arrays of wall segments supported from the outer case which extend circumferentially about the working medium flow path. The wall segments are located adjacent to the working medium flow path for confining the working medium gases to the flow path. These wall segments have radial faces which are circumferentially spaced leaving a clearance gap G therebetween. The clearance gap is provided to accommodate changes in diameter of the array of wall segments in response to operative conditions of the engine as the outer case is heated and expands or is cooled and contracts.
Examples of stator vanes used for modern gas turbine engines are shown in U.S. Pat. No. 3,989,410 issued to Ferrari entitled "Labyrinth Seal System" and U.S. Pat. No. 4,005,946 issued to Brown et al. entitled "Method and Apparatus for Controlling Stator Thermal Growth". In these constructions, the first array of stator vanes in the turbine section extends axially between the first array of rotor blades and the downstream end of the combustion chamber. In these engines, thin sheet metal seals extend between the combustion chamber and the stator vane to bound the working medium flow path. The stator vane is most advantageously rigidly bolted to either an outer support or an inner support which extend from the outer case to support the stator vane. Because of differences in thermal expansion between the inner and outer case in the radial and in the axial directions, the vane cannot be securely tied to both the inner and outer case and must be free to permit relative movement between the inner support and the outer support.
The stator vane in Brown is bolted rigidly to the outer support and slidably engages the inner support in the radial direction. The leading edge region of the support is essentially unsupported in that it carries flexible sheet metal material that join the vane to the combustion section, such as the sheet metal member 20. The vane structure shown in Ferrari is supported in a like manner being bolted at the outer support and slidably engaging the inner support at annular flange. Cooling air is ducted through an upstream conduit 48 in Brown to the stator vane to provide cooling to the interior of the stator vane. This cooling air is ducted rearwardly to downstream locations in the gas turbine engine for further cooling of adjacent portions of the engine, such as outer air seal segments. Accordingly, it is desirable to have tight sealing contact between adjacent components of the engine to prevent the leakage of cooling air into the working medium flow path.
Although the use of cooling air is accepted because it increases the service life of the airfoils of the stator vanes in comparison to uncooled airfoils, the use of cooling air decreases the operating efficiency of the engine. This decrease occurs because a portion of the engine's useful work is used to pressurize the cooling air in the compression section decreasing the amount of useful work available for output power. One way to increase operating efficiency is to decrease the leakage of cooling air from the cooling air flow paths in the engine. Another way to increase operating efficiency is to more effectively use the cooling air so that increased cooling is provided by the same amount of cooling air or so that the same amount of cooling is provided with a decreased amount of cooling air.
In particular, it is desirable to accommodate differential thermal expansion between the inner support and the outer support while still providing sealing between circumferentially extending portions of the stator vane and the adjacent supporting structure while allowing the vane to tilt in the axial direction to accommodate differences in axial growth and to slide in the radial direction to accommodate differences in radial expansion. In addition, it is desirable to divert cooling air which passes along leak paths extending between the stator vane and the adjacent stator structure to more useful purposes than flowing directly into the working medium flow path and to decrease the size of these leak paths all while accommodating differences in axial and radial growth between the inner support and the outer support for the array of stator vanes.